The present invention relates in general to substrate manufacturing technologies and in particular to apparatus for the removal of a metal oxide from a substrate and methods therefor.
In the processing of a substrate, e.g., a semiconductor substrate or a glass panel such as one used in flat panel display manufacturing, plasma is often employed. As part of the processing of a substrate for example, the substrate is divided into a plurality of dies, or rectangular areas, each of which will become an integrated circuit. The substrate is then processed in a series of steps in which materials are selectively removed (etching) and deposited. Control of the transistor gate critical dimension (CD) on the order of a few nanometers is a top priority, as each nanometer deviation from the target gate length may translate directly into the operational speed of these devices.
Areas of the hardened emulsion are then selectively removed, causing components of the underlying layer to become exposed. The substrate is then placed in a plasma processing chamber on a substrate support structure comprising a mono-polar or bi-polar electrode, called a chuck or pedestal. Appropriate etchant source are then flowed into the chamber and struck to form a plasma to etch exposed areas of the substrate.
Copper (Cu) is commonly used as to interconnect microelectronic circuits on the substrate. However, before bulk Cu deposition, some type of copper sputtering deposition process is generally required to deposit a thin seed layer (about 500 Å to about 2000 Å). A Cu seed layer generally provides the nucleation sites for the bulk Cu grain and film formation. That is, first a barrier layer may be deposited using a PVD (plasma vapor deposition) process. The Cu seed may then be deposited also using a PVD process, and finally the remaining bulk Cu may be deposited using electrochemical plating (ECP).
In general, ECP involves placing the substrate (with a Cu seed) on a plastic substrate holder. A cathode then holds the substrate with a conducting steel ring and immerses it in a plating solution containing sulfuric acid (H2SO4), copper sulfate (Cu(SO4)) and other additives. An electrical current flows form the anode, which is a copper plate to the cathode. In the solution, the Cu(SO4) disassociates to a copper ion, Cu2+, and a sulfate ion SO22−. When the copper ions are attracted to the substrate surface, where they become absorbed on the copper seed layer.
However, new approaches to Cu interconnect integration are emerging to overcome short falls of current integrations schemes. For example, one emerging technology is the use of electroless Cu plating that can replace the Copper seed and/or Cu fill. In general, an underlying barrier layer (e.g., Ti, Tin, Ta, TaN, W, WN, Ru, etc.) is catalyzed by a Pd/Sn colloid, which serves as an activator for electroless copper deposition. After activation, electroless deposition of Cu occurs on the catalytic surface. In general, the coverage of the Cu deposit reaches 100% and the adsorptive amount of Pd is greatly increased by the conditioning process. However, in order to insure uniformity, the barrier layer must substantially be free of any metal oxide they may have formed prior to the electroless Cu plating process.
A commonly known, relatively simple, and low-cost method of metal oxide removal may be the use of an atmospheric (or high pressure) plasma jet (APPJ), which generally allows a plasma to be focused on a particular location on the substrate, thus minimizing potential damage to dies on the substrate. An APPJ device generally mixes a large amount of an inert gas (e.g., He, etc.) with a small amount of a reactive gas (e.g., H2, O2, etc.) in an annular volume (e.g., tube, cylinder, etc.) formed between an rf-powered electrode (along the longitudinal axis of the source) and a grounded electrode. The generated plasma may then be forced out one end of the annular volume (plasma effluent) by pressure caused by the influx of gases (gas influent). The shape and size of the plasma effluent may be controlled by adjusting the gas influent pressure, as well as the shape and size of the discharge orifice on the APPJ device.
In addition, an APPJ may also be combined with a reactive ion etch (RIE) in order to remove the metal oxide. In general, RIE combines both chemical and ion processes in order to remove material from the substrate. Generally ions in the plasma enhance a chemical process by striking the surface of the substrate, and breaking the chemical bonds of the atoms on the surface in order to make them more susceptible to reacting with the molecules of the chemical process. Operating at ambient pressure conditions, atmospheric plasmas tend to relatively inexpensive in comparison to low-pressure plasmas that require sophisticated pumping systems to operate at near vacuum conditions. However, APPJ devices also tend to be susceptible to arcing.
An arc is generally a high power density short circuit which has the effect of a miniature explosion. When arcs occur on or near the surfaces of the target material or chamber fixtures, substantial damage can occur, such as local melting. Plasma arcs are generally caused by low plasma impedance which results in a steadily increasing current flow. If the resistance is low enough, the current will increase indefinitely (limited only by the power supply and impedance), creating a short circuit in which all energy transfer takes place. This may result in damage to the substrate as well as the plasma chamber. In order to inhibit arcing, relatively high plasma impedance generally must be maintained. A common solution may be to limit the rate of ionization in the plasma by using a large volume of inert gas at a relatively high flow rate. Another solution may be to position slots along the longitudinal axis of the powered electrode with the same electrical potential, in order to reduce the likelihood of arcing.
For example, in a common atmospheric plasma configuration, rf power creates an electrical discharge between a power electrode and a set of grounded electrodes that causes a process gas such as O2 to ionize. However, as the density of electrically charged species (i.e., ions, etc.) in the plasma increases (typically above 2%), the likelihood of destructive arcing at the exposed electrode also increases. Hence, most atmospheric plasma processes typically also comprise mostly non-electrically charged (inert) gas, such as He, which limit ionization. In a metal oxide byproduct removal application, however, the large volume (high flow) of inert gas may make the use of atmospheric plasma economically impractical.
For example, the substantial removal of a metal oxide from just a 5 mm2 surface area on the substrate may require over 10 slm (standard liters per minute) of an inert gas. This may correspond to the consumption of over 100 liters of the inert gas for a single typical 300 mm substrate. Aside from the cost of obtaining a large volume of a semi-conductor grade inert gas, the storage of such a volume in a substrate fabrication facility may be unworkable. Additionally, because of equipment cost, cleaning and recycling the inert gas may be economically impractical.
Referring now to FIG. 1, a simplified diagram of an atmospheric plasma jet device, in which both the powered electrode and the ground electrode are each configured on a cavity wall, is shown. Generally, an inert gas 118 (e.g., He, etc.) and a process gas 116 (e.g., H2, CF4, etc.) are flowed into sealed box 114 for pressurizing. The gases are, in turn, feed into a discharge chamber cavity 110 through gas influent 115, at which point a plasma is struck with an rf power source 108 and creates plasma effluent 104 from discharge orifice 117 at one end of cavity 110 to clean substrate 102. In general, the shape and diameter of discharge orifice 117 may affect the corresponding shape of plasma effluent 104 along both the lateral and longitudinal axis (e.g., laterally narrow and longitudinally deep, laterally wide and longitudinally shallow, etc.). However, as previously stated, a large volume of inert gas may be required to prevent the generation of arc 105 between powered electrode 106 to grounded electrode 112.
Referring now to FIG. 2, a simplified diagram of an atmospheric plasma jet device, in which a powered electrode is configured as a center rod and a grounded electrode(s) is configured on a cavity inner surface, is shown. As before, generally, an inert gas 118 (e.g., He, etc.) and a process gas 116 (e.g., CF4, H2, etc.) are flowed into sealed box 114 for pressurizing. The gases are, in turn, feed into a discharge chamber cavity 110 through gas influent 115, at which point a plasma may be struck with an rf power source 108 and creates plasma effluent 104 from discharge orifice 117 at one end of cavity 110 to clean substrate 102. In general, the shape and diameter of discharge orifice 117 may affect the corresponding shape of plasma effluent 104 along both the lateral and longitudinal axis (e.g., laterally narrow and longitudinally deep, laterally wide and longitudinally shallow, etc.). However, as previously stated, a large volume of inert gas may be required to prevent the generation of arc 105 between powered electrode 106 to grounded electrode 112.
In view of the foregoing, there are desired apparatus for the removal of a metal oxide from a substrate and methods therefor.